Iranian Naft Airlines, a homebound charter airline providing passenger and cargo services to Iran’s Ministry of Petroleum, says it has received the first Boeing jet.

The aircraft, one of the four Boeing 737 single-aisle jetliners bought from the US aviation company, was delivered to Naft Airlines on Sunday, its Managing Director Nurollah Rezai Niyaraki said.

“After the JCPOA (Joint Comprehensive Plan of Action), an agreement was signed with the Boeing company for purchase of four 737s and today one of the ordered aircraft was delivered to Iranian Naft Airlines,” he told Shana news agency.

The aircraft took off at 1700 hours local time on its first flight from Tehran to Ahvaz on Sunday, the official said.

“According to the timeline, the remaining three Boeing 737s will gradually join the Iranian Naft Airlines fleet at specific dates” by the end of the current Iranian year on March 20, 2017, Rezai Niyaraki added.

Other Iranian media reports said the aircraft, with a capacity to carry up to 148 passengers, had been leased to Iran under the complete crew, maintenance, and insurance (ACMI) arrangement.

A Fokker 100 operated by Iranian Naft Airlines flies over Tehran with Alborz mountains in the background.

The reports, however, did not clarify whether the aircraft was a brand new or used plane and whether it had been leased directly by Boeing or another airline.

In June, Boeing signed a memorandum of agreement with Iran Air to sell a total of 80 aircraft and lease a further 29 to the company in a potential deal worth about $25 billion.

The plan, however, faces stiff opposition in US Congress, raising doubts about deliveries of the jets that are scheduled to start in 2017 and run through 2025.

On Monday, Deputy Minister of Roads and Transportation Asghar Fakhriyeh Kashan said Iran may take one aircraft off the provisional deal with Boeing as he criticized what Tehran sees as unfair delays in finalizing it.

The tentative agreement awaits US Treasury Department’s endorsement before being finalized.

Under the nuclear deal, the Treasury Department will review on a case-by-case basis the licensing of individuals or entities that want to export, re-export, sell, lease or transfer to Iran commercial passenger aircraft, and associated parts and services.

Naft Airlines appears to be the first Iranian company to have its deal cleared by the US Treasury’s Office of Foreign Assets Control (OFAC).

Iranian airlines have some 60 Boeing airplanes in service, but most of them were purchased before the 1979 Islamic Revolution and are in a dire need of repair or retirement.